Since prostaglandin (hereinafter referred to as PG) shows various important physiological actions in a trace amount, natural PG analgogues and a vast number of derivatives thereof have been studied on synthesis and biological activities, with attempts to apply these compounds to pharmaceuticals. In particular, PGE.sub.1 has characteristic actions such as platelet aggregation inhibition, blood pressure lowering and the like and is already inpractical use as a drug for ameliorating peripheral circulatory disturbance. Therefore, a large number of PGE.sub.1 analogues have been investigated. Hitherto known PGE.sub.1 anologues, however, have a drawback of quick metobolism in living body and consequent short term effect. Further, hitherto proposed PGE.sub.1 analogues induce diarrhea as a side effect when administered orally and accordingly have a problem in that they cannot be administered orally in a sufficiently high amount to obtain the satisfactory effects.
Meanwhile, 13,14-didehydro-PGE.sub.1 methyl ester and 6-hydroxy-13,14-didehydro-PGE.sub.1 are known as 13,14-didehydro-PGE.sub.1 analogues obtained by converting the double bond between the 13- and 14-positions of PGE.sub.1 to a triple bond [Japanese Patent Application Kokai (Laid-Open) No. 100446/1977 and U.S. Pat. No. 4,131,738].
The main object of the present invention is to provide novel PGE.sub.1 analogues which have a higher efficacy, a more prolonged action and a lower side effect then hitherto known PGE.sub.1 analogues.